Dear Friend,

Upon a lengthy storage under aerobic conditions chloroform is converted slowly to phosgene (COCl2), releasing HCl in the process.

2 CHCl3 + O2 → 2 COCl2 + 2 HCl

To prevent such reaction, commercial chloroform is stabilized with ethanol or amylene. Phosgene and HCl can be removed from chloroform by washing with saturated aqueous carbonate solutions, such as sodium bicarbonate. This procedure is simple and results in harmless products. Phosgene reacts with water to form carbon dioxide and HCl, and the carbonate salt neutralizes the resulting acid.

Suspected samples can be tested for phosgene using filter paper (treated with 5% diphenylamine, 5% dimethylaminobenzaldehyde in ethanol, and then dried), which turns yellow in phosgene vapor. There are several colorimetric and fluorometric reagents for phosgene, and it can also be quantified with mass spectrometry.

Further, if traces amounts of HCl are present the latter may react with Ca(CO3)2 to furnish CaCl2, CO2 and water.

Please note that it might be difficult to observe changes upon titration of (tiny amounts) traces of HCl with silver nitrate.

Hoping this will be helpful,

Rafik

The problem is not in the presence of impurities in trichloromethane. Trichloromethane can be hydrolyzed in the presence of traces of water. Since there is a stabilizer also (ethyl alcohol, it interferes with the formation of phosgene - product of CCl3 oxidation), it can be subjected to alcoholysis too. As a result, calcium chloride can form from the carbonate.

Carry out the same analysis for the chloride ion (or even for calcium, which is even easier and cheaper) with the extraction (by distilled water) of solution after mixing calcium carbonate with chloroform and complete sedimentation of the suspension. Carbonate itself should not dissolve in chloroform. But traces of calcium chloride in the liquid phase should appear.

16 Ca H CI O9 + 4 C2 H 6 O yields 2 C H Cl3 + 3

Please , also describe temperatures.

If you do not have an acid present to yield H2CO3, than no reaction. Also it is important the pH in the aqueous pahse.

Dear Friend,

Upon a lengthy storage under aerobic conditions chloroform is converted slowly to phosgene (COCl2), releasing HCl in the process.

2 CHCl3 + O2 → 2 COCl2 + 2 HCl

To prevent such reaction, commercial chloroform is stabilized with ethanol or amylene. Phosgene and HCl can be removed from chloroform by washing with saturated aqueous carbonate solutions, such as sodium bicarbonate. This procedure is simple and results in harmless products. Phosgene reacts with water to form carbon dioxide and HCl, and the carbonate salt neutralizes the resulting acid.

Suspected samples can be tested for phosgene using filter paper (treated with 5% diphenylamine, 5% dimethylaminobenzaldehyde in ethanol, and then dried), which turns yellow in phosgene vapor. There are several colorimetric and fluorometric reagents for phosgene, and it can also be quantified with mass spectrometry.

Further, if traces amounts of HCl are present the latter may react with Ca(CO3)2 to furnish CaCl2, CO2 and water.

Please note that it might be difficult to observe changes upon titration of (tiny amounts) traces of HCl with silver nitrate.

Hoping this will be helpful,

Rafik

Thank you all for your answers. I have some calcium carbonate as impurity in my sample. I dissolve polycarbonate in either chloroform or dichloromethane (DCM) at room temperature overnight and then melt mix it with PET. The results vary significantly based on the solvent I use! I suspect that calcium carbonate reacts with some decomposition products of chloroform and affects the transesterification reactions between PET and PC (perhaps as a catalyst). Chloroform stabilized with amylene also showed the same results as chloroform containing ethanol. If I add HCl to DCM I don't get the same result as chloroform so probably it is something other than HCl and calcium chloride. Even without adding the nanoparticles with CaCO3 impurity, dissolving PC in chloroform slightly affects the transesterification reactions! The lable on the bottle says it contains less than 0.05 ppm lead (Pb). Can lead impurity in chloroform cause such a huge effect? Lead impurity from chloroform is about 0.00001 wt% in the final sample!

Can calcium carbonate accelerate decomposition of chloroform? Is there any possibility for calcium hypochlorite to form?

Dear Friend,

Generally, the reaction of calcium carbonate with chloroform to form calcium hypochlorite is NOT affordable. In contrast the reverse reaction is likely to happen:

2Ca(ClO)2 + 2CO2 → 2CaCO3 + 2Cl2 + O2

In order to prevent any side reaction during the executing of your procedure I suggest to distill the chloroform and to use it freshly after distillation. Alternatively you can use distilled DCM since this compound is relatively much more stable than CHCl3. The reaction with DCM is expected to have less side reactions. Lead in the indicated concentrations is expected NOT to have any effect on the desired reaction.

P.S. It is advisable to treat the chloroform to be used in the reaction with sodium carbonate or sodium bicarbonate to neutralize any HCl present, and then to distill the chloroform and to use it freshly.

Hoping this will be helpful,

Rafik

Dear Prof. Karaman,

Thanks a lot for your answer. Actually the unknown reactions that happen between CaCO3 and chloroform have a favorable effect on some properties of the nanocomposite, Therefore I do not want to remove the decomposition products from chloroform. I am just looking for a mechanism to explain the strange results. The results obtained from adding 1 v/v% HCl to DCM did not resemble those form chloroform so I don't think CaCl2 is the chemical that cause those different results between chloroform and DCM.

Dear Friend,

The difference between dichloromethane and chloroform is recognized through their acidity; where the pKa of chloroform is about 25 and that of dichloromethane is about 39. Chloroform is more acidic than dichloromethane.

Chloroform reacts with sodium hydroxide to yield the intermediary dichlorocarbene, sodium chloride and water.

HCCl3 + NaOH → CCl2 + NaCl + H2O

Dichlorocarbene is unstable in these conditions and reacts with additional sodium hydroxide to yield sodium formate in a process which is best aided by a phase transfer catalyst such as ethanol:

CCl2 + 3NaOH → HCOONa + 2NaCl + H2O

I believe that the reaction of dichloromethane with such base ismuch slower and needes more harsh conditions.

Further, calcium carbonate is a weaker base than sodium hydroxide but it might play the same role as indicated for sodium hydroxide.

Please note, if the reaction described above occurs with calcium carbonate the carbenic product (dichlorocarbene) is a very reactive intermediate that is capable of accelerating a variety of unexpected side reactions.

Hoping this will be helpful,

Rafik

Dear Prof. Karaman,

Thank you so much for taking the time to answer in such detail. It seems that chloroform is degraded faster in the presence of calcium carbonate which probably forms calcium hydroxide (or maybe the stronger base, ethoxide from ethonal). If I add calcium chloride to DCM the results are to some extent similar to chloroform but adding HCl to DCM changes nothing so it seems that it is the calcium itself that reacts with some chemical from decomposition products and remains in the casted film as a salt (I dry the film at 130 C). Can calcium chloride accelerate decomposition of DCM as well? Why does only calcium chloride affect the results and not the HCl which is supposed to form calcium chloride by reacting with calcium carbonate?

I forgot to mention that I first sonicate nanoparticles with CaCO3 impurity in chloroform (or DCM) for 2 hours and then add the dispersion to PC solution, therefore there is a higher probability for degradation of the solvents.

One factor you may not have under control is exposure to light. The reaction of chloroform or DCM with dissolved oxygen is photochemical: in the absence of anything to react with the phosgene produced, you can get significant amounts of phosgene. This won't happen here, because you've got stabilisers present - but the decomposition of the chlorinated solvents will still take place in light. I suggest you try excluding light to see if it makes any difference.

Dear Friend,

To check whether your suggestion on the involvement of calcium chloride (calcium ions via the addition of calcium carbonate) in driving the process to yield the unknown products (which luckily you wish) when the process is carried out in chloroform but not in dichloromethane, I suggest to run the sonication step with sodium carbonate (instead of calcium carbonate) once using chloroform and another using dichloromethanes as solvents. The results of these two experiments should give you a good picture on the the role or involvement of calcium ions in the process.

Good luck,

Rafik